EP0570500B1

EP0570500B1 - Reamer

Info

Publication number: EP0570500B1
Application number: EP92906386A
Authority: EP
Inventors: W.E.Michael Mikhail
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-02-08
Filing date: 1992-02-06
Publication date: 1998-12-02
Anticipated expiration: 2012-02-06
Also published as: EP0570500A1; ZA92876B; US5284482A; CA2101941A1; AU651044B2; DE69227761D1; CA2101941C; JP2567191B2; ATE173908T1; AU1376092A; US5180384A; EP0570500A4; DE69227761T2; WO1992013503A1; JPH06507325A

Abstract

A universal patellar clamp is disclosed. The clamp includes an articular surface clamping member having a central aperture defining a centerline axis. The central aperture is sized to accept all available known sizes of cannulated reamers. An anterior clamping member is positioned along the centerline axis and is movable with respect to the articular clamping member to effect clamping of the patella. A pair of guide arms are engaged with the articular clamping member to be positioned over the central aperture and provide a guide hole for supporting a threaded guidewire or pin along the centerline axis. The guide arms are removable from their position over the central aperture to clear the aperture for access by the cannulated reamer.

Description

The present invention is directed to a reamer.

In total knee replacement surgery, a prosthesis is provided in which one component is fastened to the distal end of the femur which has been resectioned and another component is fastened to the proximal end of the tibia which has been resectioned so that the two components will act together in permitting the leg to bend and straighten out. In performing such surgery, the patella is not normally replaced but rather is resected such that the interior crown portion facing the condyles is cut and reamed to form a cavity in which a patellar prosthesis is implanted. The patellar prosthesis has a crown facing inwardly to engage the patellar or trochlear groove of the femoral component.

US 4,341,206 describes a cannulated tool for forming a stepped blind hole for receiving a fracture reducing implant. The tool comprises a small diameter drill portion axially adjustable with respect to a larger diameter reamer portion. A conical portion includes cutting surfaces to chamfer the entrance of the hole and also includes non-cutting portions which serve to limit penetration of the tool into the bone. The tool has particular application to fractures of the neck of the femur.

Heretofore, in preparing a patella for an implant, it was necessary to engage the patella with a clamp having a circular cross-sectional configuration and, using the interior surface of the clamp as a guide, ream a cavity in the patella of sufficient size to receive the patella implant intended to be used. Depending upon a number of factors including the size of the patient, the patellar implant could be one of a number of different sizes. As a result of this, it was necessary to have available a number of clamps each having a different diameter for guiding various size reamers. Typical prior art methods of forming a Cavity for implanting a patellar prosthesis are shown and described in the following publications,: Brochures entitled "The AMK Total Knee System Design nationale and Surgical Procedure" (page 25), DePuy, Division of Boehringer Mannheim Corporation, Warsaw, Indiana, and "WHITESIDE ORTHOLOC ® Modular KNEE SYSTEM", copyright 1989 by Dow Corning Wright, Arlington, Tennessee.

There has recently been introduced a new design of patellar prosthesis having a tapered surface on the side away from the crown. One such prosthesis is the subject matter of US-A-5,197,986, filed October 18, 1990, by the applicant herein. The reamer of the present invention may be used for implanting a patellar prosthesis, it is well-suited for implanting patellar prostheses of the type disclosed in such patent application; however, it should be understood that the reamer of the present invention is not so limited and may be used for implanting a wide variety of patellar prostheses. It has a significant advantage over the prior art in that the reamer of the present invention does not rely upon a patella clamp to guide the reamer. Accordingly, in utilizing the reamer of the present invention, it is not necessary to have available a plurality of clamps of varying sizes.

The present invention provides a new reamer for preparing a human patella for implanting a patellar prosthesis therein. A new method for implanting a patellar prosthesis in a human patella using the reamer is also described. As is well-known in performing knee replacement surgery, the patella is everted and retained in a position permitting the surgeon to have access to the articular surface which is normally engaged in the intercondylar notch between the condyles. With the patella so supported, the surgeon, using a saw or similar tool for performing osteotomy, removes the top portion of the articular surface, thus leaving a flat surface near the central portion of the patella. Desirably, only a small portion of the articular surface is removed in order to leave as much of the original patella intact as possible. Thus, it is desirable that as little of the human patella be removed as possible.

Following removal of the top of the articular surface a thread guide wire or pin is used to drill a passageway in the central portion of the patella at substantially right angles to the flat surface. Then, using the threaded guide wire which may be left in the passageway or a rod of similar size to that of the threaded guide wire positioned in said passageway, the cannulated reamer of the present invention is placed over the threaded guide wire or other guide rod and, using such threaded guide wire or guide rod as a guide, the reamer is utilized to ream thereby forming a cavity having a size and configuration suitable for receiving the patellar prosthesis. Following such reaming, the cavity is cleaned, bone cement placed therein and the patellar prosthesis implanted therein. If desired, the reaming could be performed in stages, initially using a reamer sized to form a relatively small cavity and thereafter using a reamer sized to form the cavity for receiving the patella prosthesis.

It is also within the contemplation to drill the passageway without cutting the apex of the articular surface or otherwise forming a flat surface.

Accordingly, it is an object of the present invention to provide a reamer for reaming a cavity in a human patella for receiving a patella prosthesis, which minimises the amount of bone needed to be removed.

It is a further object of the present invention to provide a reamer wherein the central passageway is sized to receive a guidewire to accurately guide the reamer.

It is a further object of the present invention to provide a reamer wherein the stem has an enlarged area for engagement with a rotatable power source for rotating the head and cutting blades.

It is a further object of the present invention to provide a reamer wherein the cutting means comprise a first cutting edge adjacent to the head and parallel to the passageway, a second cutting edge extending from the first cutting edge, tapering inwardly towards the passageway and away from the head, a third cutting edge substantially parallel to the passageway and a fourth cutting edge extending radially inwardly from the third cutting edge and joined to a housing for reaming a cavity of a size and shape suitable for receiving the specific patellar prosthesis intended for implantation.

Other objects and advantages of the present invention will become apparent from the following detailed description in conjunction with the attached drawings.

Fig. 1 is an elevational view showing a cannulated reamer having cutting knives of a configuration suitable for implanting one type of patellar prosthesis.

Fig. 2 is a top plan view of the cannulated reamer of Fig. 1.

Fig. 3 is a bottom plan view of the cannulated reamer of Fig. 1.

Fig. 4 is a sectional view taken along line 4-4 of Fig. 1.

Fig. 5 is a fragmentary sectional view of the reamer head taken along line 5-5 of Fig. 3.

Fig. 6 is an elevational view showing the threaded guide wire for forming a guide passageway in the patella.

Fig. 7 is an end view of the threaded guide wire of Fig. 6 looking in the direction of the arrows 7-7.

Fig. 8 is a view similar to Fig. 3 showing a modified reamer.

Fig. 9 is a fragmentary elevational view of the modified reamer of Fig. 8.

Fig. 10 is a sectional view of a patella during the initial step of removing the apex of the articular surface to form a flat surface.

Fig. 11 is a view similar to Fig. 10 showing the next step of drilling a passageway at substantially right angles to the flat surface formed as shown in Fig. 10.

Fig. 12 is a view similar to Fig. 11 showing the reaming step using the drill bit or other guide rod to guide the reamer during reaming.

Fig. 13 is a sectional view showing a patellar prosthesis implanted in a patella prepared in accordance with the present invention.

Fig. 14 is a sectional view of a patella during the initial step of a modified method of preparing, a patella wherein a passageway is formed without first forming a flat surface.

Fig. 15 is a view similar to Fig. 14 showing one of a plurality of reaming steps using the threaded guide wire or other guide rod to guide the reamer during reaming.

Fig. 16 is a view similar to Fig. 15 showing the second reamer beginning to ream the final cavity.

Fig. 17 is a view similar to Fig. 16 showing completion of reaming the final cavity.

Fig. 18 is a sectional view showing a patellar prosthesis implanted in a patella prepared using the reamer of the present invention.

Referring now to Figs. 1-5, there is shown a reamer generally designated by numeral 10 having, a head 12 mounted on the end of a cannulated stem 14 extending along an axis A. The head 12 has a upper surface 13 and a lower surface 15. A cutting assembly 16 extends downwardly from the head 12 and includes a housing 18 and a plurality of cutting blades 20 integrally formed with and extending radially outwardly from the housing 18. In the embodiment of Figs. 1-5, four cutting blades 20 are provided at substantially 90° from each other. As can be seen particularly in Fig. 1, the shape of the cutting blades are substantially identical and have a configuration tailored to form a cavity of a size and shape suitable for receiving, the specific patellar prosthesis intended for implantation.

For example, referring briefly to Fig. 13, there is shown a patella P in which a cavity 22 has been reamed and in which a patellar prosthesis 24 has been implanted. The patellar prosthesis 24 of Fig. 13 has a body portion 26 with a dome 28 facing away from the patella P in a position to engage the patellar or trochlear groove of the femoral component of a total knee implant (not shown). The dome 28 terminates at its outer periphery at an edge 30 which defines a circle from which a short cylindrical wall section 32 depends. As can be seen in Fig. 13 the edge 30 is preferably above the upper surface of the patella P about 1-2 mm; however, it could meet the upper surface of the patella and thus provide a smooth transition between the dome 23 and the upper surface of the patella P.

Tapering inwardly toward the central axis and downwardly in a direction away from the dome 28 is an inner wall surface 34 from which a stem 36 depends. The stem 36 may have one of a wide variety of shapes. A layer Of bone cement 37 such as polymethylmethacrylate is used to bond the patellar prosthesis 24 in the cavity.

As will be appreciated from viewing Fig.1 and Fig. 13, the cross-sectional shape of that portion of the patellar prosthesis 24 facing away from the dome 23 determines the shape defined by the cutting, blades 20 and the shape of the cavity to be formed thereby. Thus, each of the blades 20 has a first cutting edge 20a substantially parallel to the Axis A of the stem 14, a second cutting edge 20b tapering inwardly toward such axis A and away from the head 12, a third cutting edge 20c substantially parallel to such axis and a fourth cutting edge; 20d extending radially inwardly from the third cutting edge 20c and joined to the housing 18. It should be understood, however, that the shape of the cutting blades 20 may vary depending upon the configuration of the patellar prosthesis intended to be implanted. In forming a cavity of the configuration shown in Figs. 12 and 13 for receiving the prosthesis 24, the third cutting edge 20c and fourth cutting edge 20d will form a lower cylindrical portion of the cavity 22 intended to receive the stem 36, the second cutting edge 20b will form the portion of the cavity 22 flaring upwardly and outwardly from the lower cylindrical portion for receiving the portion of the prosthesis defined by the tapering inner wall surface 34 and the first cutting edge 20a will form the upper cylindrical portion of the cavity 22 for receiving the short cylindrical wall section 32 of the patellar prosthesis 24.

As can be seen in Figs. 1 and 12, the cutting blades 20 do not extend outwardly to the outer periphery of the head 12. Thus, the first cutting edge 20a is closer to the axis A than is the outer periphery of the head 12. This construction permits the lower surface 15 to contact the patella P and function as a stop for determining the proper depth for the cavity 22 and insure against inadvertent reaming to an excessive depth.

The reamer 10 has a cylindrical passageway 40 extending throughout the stem 14, head 12 and housing 18. Additionally, the head 12 has a plurality of inclined passageways 42 extending therethrough from a position on the lower surface 15 between the cutting blades 20 and extending out of the upper surface 13. These inclined passageways 42 are intended to provide a means for expelling the debris from the cavity 22 being reamed. Thus, as the blades 20 ream the patella P, the bone material cut therefrom will be propelled into the end of the inclined passageway 42 at the lower face 15, through inclined passageway 42 and out of it at the upper face 13.

The stem 14 of the reamer 10 has an enlarged area 44 which may be provided with opposing flat surfaces 45 for engagement by rotatable power means for rotating the head 12 and the cutting blades 20 carried thereby.

Referring now to Figs. 6 and 7, there is shown a threaded guide wire 50 having a cutting head 52, a helical thread 54 and an elongated shank 56 having a diameter slightly smaller than that of the cylindrical passageway 40 and a length sufficiently long to extend completely through the stem 14 of reamer 10. The cutting head 52 has three triangular shaped flats 58 extending to a tip 60 with the edges between the adjoining flats 58 functioning as the primary cutters.

Figs. 8 and 9 show a modified reamer 10' having a head 12' with eight cutting blades 20' as contrasted with the previous embodiment having four cutting blades 20. In this embodiment, there are provided eight inclined passageways 42' extending through the head for expelling debris during the cutting operation.

Referring now to Figs. 10-12, there is shown a human patella P having an articular surface including an apex 70 which, in a normal knee, engages the intercondylar notch between the condyles at the distal end of the femur. The top of the apex 70 is cut with a standard cutting blade 72 to form a substantially planar surface 74 as shown in Figs. 10 and 11. Thereafter, the threaded guide wire 50 powered by a drill (not shown) is utilized to drill a passageway 76 in the patella P.

Following drilling of the passageway 76 the drill is disconnected from the threaded guide wire 50, leaving the threaded guide wire 50 in the passageway 76. Then, using the threaded guide wire 50 as a guide, the reamer 10 is placed thereover and is connected to power means which rotate it thereby causing the cutting blades 20 to form the cavity 22 having a configuration determined by the configuration of the cutting edges 20a, 20b, 20c and 20d of cutting blades 20. In the drawings it is shown as having the desired configuration to receive the patellar prosthesis 24. During such cutting the threaded guide wire 50, snugly received in the passageway 40, serves to accurately guide the reamer 10 on the correct axial path in reaming the patella P to form the cavity 22. Thus, the threaded guide wire 50 prevents the reamer 10 from drifting off such path and forming a larger cavity than desired. As previously noted, during such reaming process, debris will be expelled through the included passageways 42 extending through the head 12. Completion of the reaming step occurs when the lower surface 15 of the head 10 engages the patella P. As previously noted, the design of the reamer head 12 to cause engagement of such lower surface 15, prevents the reamer from reaming to a greater depth than desired.

Following completion of the reaming step, the reamer 10 and the threaded guide wire 50 are removed, the cavity 22 is cleaned of debris and prepared in accordance with standard implantation techniques including application of bone cement such as polymethylmethacrylate and affixing of the patellar prosthesis 24 therein. Preferably, prior to placing bone cement in the cavity 22, pulverized bone chips and/or bone slurry will be placed in the end portion 76a of the passageway 76 extending below the bottom of that portion of the cavity 22 formed by the lower cutting edge 20d. Such bone chips and/or bone slurry serve as a graft, inducing bone growth into such end portion 76a. However, it is possible that such end portion be filled only with bone cement.

Irrespective of whether the cutting head has four cutting blades 20 shown in the embodiment of Figs. 1-5, or eight cutting blades 20' shown in the embodiment of Figs. 8 and 9 or fewer or more of such cutting blades, the reamer of the present invention permits the implantation of a patellar prosthesis in a highly accurate manner with a minimal removal of bone.

Referring now to Figs. 14-18, there is shown a modified method for preparing a patella P' and for implanting a patellar prosthesis 24' therein.

As shown in Fig. 14, there is provided a threaded guide wire 50' having a head 52' with cutting flats 58' extending to a tip 60'. A helical thread 54' extends upwardly from the head 52'.

Under this embodiment, the apex 70' of the patella P' is not cut to form a flat surface as in the previous embodiment, but rather the threaded guide wire 50' directly engages the articular surface at a desired location in the vicinity of the apex 70. As will be appreciated by those skilled in the art, during this step, the patella P' will be held by a suitable clamping mechanism while the drill powering, the threaded guide wire 50' is used to form a Passageway 76' in the patella P'.

The drill is then disconnected from the threaded guide wire 50' and a first or pilot reamer 90 having a head 92 mounted on the end of a cannulated stem 94 is positioned over the threaded guide wire 50'. The head 92 has a plurality of cuttings blades 96 extending downwardly therefrom. As can be seen from Fig. 15, the head 92 and cutting blades 96 of the pilot reamer 90 are much smaller than required to form a cavity of the size intended for the patellar implant 24' as shown in Fig. 18. Thus, the first or pilot reamer 90 forms a relatively small cavity 98. As shown in Figs. 16 and 17, a second reamer 10'' similar or identical to the reamer 10 of the embodiment of Figs. 1-5 is provided to form a final cavity 99 having a size and configuration suitable for receiving the patellar implant 24'. It may be preferable perform the reaming in two steps, particularly if it is preferred not to form a flat surface by cutting the apex of the articular surface. In performing the reaming in two steps, a first relatively small cavity 98 is formed using the threaded guide wire 54' or other guide means positioned in the passageway 76' to guide the direction of the first or pilot reamer 90 and thereafter final cavity 99 is formed with reamer 10' again using the threaded guide wire 50' or other guide means. As in the previous embodiments the end portion 76a is preferably filled with bone chips or bone slurry to serve as a graft, inducing bone growth therein.

Although a cannulated reamer 10 with flat cutting blades 20 has been described it should be understood that a wide variety of reamers could be used. For example, a convex grater type reamer with a cannulated center to accommodate the guide wire is one which could be used.

Many modifications and embodiments will become readily apparent to those skilled in the art. Accordingly, the scope of the present invention should be determined only by the scope of the appended claims.

Claims

A reamer (10) comprising a stem (14),a head (12) with upper (13) and lower (15) sides, cutting means (20) integral with and depending from the lower side, said cutting means defining a first radial extent of first size, and a central passageway (40) extending through the stem, head and cutting means, said lower side (15) defining a second radial extent of second size larger than said first size and forming stop means which determine the depth of a reamed cavity, said head (12) having an aperture (42) defining an inclined passageway between an inlet at the lower side (15) and an outlet at the upper side (13), said inlet being spaced from said cutting means (20).
A reamer (10) as claimed in claim 1, wherein the central passageway (40) is sized to receive a guide wire (50).
A reamer (10) as claimed in any preceding claim, wherein the stem (14) has an enlarged area (44) for engagement with a rotatable power source.
A reamer (10) as claimed in any preceding claim, wherein the cutting means (20) comprise a first cutting edge (20a) adjacent to the head and parallel to the passageway, a second cutting edge (20b) extending from the first cutting edge, tapering inwardly towards the passageway (40) and away from the head, a third cutting edge (20c) substantially parallel to the passageway (40) and a fourth cutting edge (20d) extending radially inwardly from the third cutting edge (20c) and joined to a housing (18).
A reamer (10) as claimed in any preceding claim, in combination with an elongated guide wire (50).
A reamer as claimed in claim 5, wherein the guide wire has a helical thread (54).
A reamer as claimed in claim 5 or 6, wherein the guide wire has a cutting head (52).